1. Technical Field of the Invention
The present invention relates to novel cinnamamide, benzalmalonamide and benzalmalonate compounds bearing short-chain silicone substituents on the aromatic moieties thereof.
This invention also relates to compositions of matter, in particular cosmetic compositions, comprising the above novel compounds, which are especially well suited for the photoprotection of the skin and/or the hair against the deleterious effects of UV radiation, in particular solar radiation.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that light radiation of wavelengths more particularly of from 280 to 320 nm, i.e., UV-B irradiation, causes skin burning and erythema which can impair the development of a natural tan. For these reasons, as well as for aesthetic reasons, there is an increasing demand for means of controlling this natural tanning in order to thereby control the color of the skin. This UV-B radiation must thus be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths of from 320 to 400 nm, which tan the skin, also adversely affects it, especially in the case of sensitive skin or skin which is continually exposed to solar radiation. UV-A rays especially cause a loss in the elasticity of the skin and the appearance of wrinkles, promoting premature skin aging. Such irradiation promotes triggering of the erythemal reaction or amplifies this reaction in certain individuals and may even be the source of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons, such as conservation of the natural elasticity of the skin, for example, an ever-increasing number of individuals wish to control the effect of UV-A rays on their skin, it is desirable to also screen out UV-A radiation.
A wide variety of compounds suited for photoprotection (UV-A and/or UV-B) of the skin are known to this art.
Most of these are aromatic compounds exhibiting absorption of UV radiation in the region from 280 to 315 nm, or in the region from 315 to 400 nm, or in both of these regions. They are typically formulated into antisun or sunscreen compositions which are in the form of an emulsion of oil-in-water type (namely, a cosmetically acceptable vehicle, diluent or carrier comprising a dispersing continuous aqueous phase and a dispersed discontinuous oily phase) and which thus contain, in various concentrations, one or more conventional lipophilic and/or hydrophilic organic screening agents including an aromatic function. These are capable of selectively absorbing harmful UV radiation, such screening agents (and their amounts) being selected as a function of the desired sun protection factor SPF (the sun protection factor being expressed mathematically by the ratio of the irradiation time required to attain the erythema-forming threshold with the UV screening agent to the time required to attain the erythema-forming threshold in the absence of UV screening agent).
Other than their screening power, these compounds exhibiting anti-UV activity must also have good cosmetic properties in compositions comprised thereof, good solubility in the usual solvents, and in particular fatty substances such as oils and greases, as well as good resistance to water and to perspiration (remanence).
Among all of the aromatic compounds which are suited for this purpose, particularly well suited are the silicon-containing benzalmalonate compounds described in EP-A-358,584 and in EP-A-392,882, both assigned to the assignee hereof. Admittedly, these compounds have good liposolubility. However, they also comprise very long silicone chains and, taking account of their bulk, their synthesis, as well as their formulation into cosmetic compositions, is not without difficulty. Lastly, their cosmetic properties are not always satisfactory.